How large is too big and other stove questions for the one I'm building

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Poodleheadmikey

New Member
Feb 20, 2011
68
Southern New Jersey
Can it be "too big" over all?

What about in one dimension? Disproportionately "too big"?

Mine right now is going to be 19" wide by 26" deep by about 20" tall - to the smoke shelf.

Those are all 'inside the fire brick' dimensions.

Of course I could add brick to reduce the height.

PHM
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I am bricking the floor and about 8" up the side and rear walls.

What about across the front wall? Under the loading door. Will fire brick under the loading door be a benefit to the stove?

Or will incoming combustion air make that area too cool anyway?

BTW: is there any real benefit to pre-heating the combustion air to the stove?

PHM
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Thanks, but I know how to design a fireplace properly. Or rather; I know that fireplace design is critical and where to look up the correct information. <g>

But I was asking in regard to the enclosed fire box of a steel wood stove.

Can that be made too large ? Or perhaps disproportionally and detrimentally large in one dimension?

PHM
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Too large for what? One design may be too large for a house, but great for the pole barn. The firebox size mentioned is big, but if you are heating and open plan, 3000 sq ft space it might be ok. Or just perfect for the 24' sq cabin that wants to be a sauna.

The firebox seems a bit tall. You probably won't be filling it that high. Will it have two courses of firebrick on the sides? If not, I would lower the height. How far would depend, will there be secondary tubes under the baffle?

PS: Do you have any books on stove design or wood burning? Some early texts by Jay Shelton might be helpful.
 
Merged threads so that questions in one aren't answered in another thread.

It's good to preheat the secondary air. if possible.
 
Poodleheadmikey said:
Can it be "too big" over all?

What about in one dimension? Disproportionately "too big"?

Mine right now is going to be 19" wide by 26" deep by about 20" tall - to the smoke shelf.

Those are all 'inside the fire brick' dimensions.

Of course I could add brick to reduce the height.

PHM
-----
Click to expand...

One way to look at it is to consider the challenge of burning a stack of splits (1) completely and (2) efficiently. As we all know, achieving any of these two objectives is easy.

If you only want to burn completely (and thus cleanly), just space the splits a bit from each other, create a strong, forced airflow (remember the old bellows used by all smiths) and light off quickly (perhaps using a propane feeder flame). You should be able to create a very hot fire and have only ashes left within a few hours (or even minutes). However, if you make up the energy balance of this process, it will become clear that most of the heat must have gone out of the chimney. Also, you have to add in the energy cost of maintaining a forced air flow and possibly even feeder flames (to keep everything burning evenly and reduce areas where pyrolysis and gasification temporarily lead to the formation of incomplete combustion products).

If you only want to burn efficiently (in terms of BTUs delivered to the home per pound of dry wood), you will first of all need to maximize the chance that every oxygen molecule will be able to find one or two fuel (i.e. wood) molecules to react with. All oxygen that flows through the combustor without ever touching a hot wood or wood gas molecule reduces the efficiency of the combustion process. Especially, because it will carry 5+ times its own volume in hot air along, not to mention added hot water vapor.

A fire box that is much larger than the bundle of wood being burned will automatically increase the chance that many of the oxygen/air molecules flowing through will never collide with a combustible wood or wood gas molecule (particularly if the excess size will be reflected in a larger cross-sectional area perpendicular to the main direction of the air flow). Providing a second chance for that to happen by means of a catalytic afterburner will help, of course, but a catalytic surface can only accommodate a limited number of oxygen molecules; the rest will simply flow through.

Throttling the total air flow through the fire box back to provide oxygen molecules with a better chance to find hot wood or wood gas molecules will soon slow the overall combustion process down to a point that large amounts of incompletely burned products, ranging from carbon monoxide to creosote and soot, will be formed. Again, a catalytic afterburner will provide a second combustion chance but, at some point, will be overwhelmed and you will start losing energy not only in the form of heat but also in the form of unburned carbon (and associated hydrogen).

In the case of overly large fireboxes it will be more difficult to achieve high energy efficiencies if the dimensions perpendicular to the direction of the air flow are unnecessarily large. However, as already hinted at by the OP, if the excess size will primarily be in a direction ALONG the direction of the air flow the extra firebox wall surface area created might conceivably be put to good use for cooling off the flue gases, producing more convective heat and/or even allowing space for heating and cooking purposes (by direct conductive heating), as was common with some of the old stove designs.

In the case of unusually deep fireboxes, it might be worthwhile to make sure that the wood is placed close to the front and that the rear section is equipped with baffles to help prevent back flows (as well as promote heat exchange with the environment). In case the heat exchange processes in the deeper parts of the stove cool the flue gases too much, it might be advisable to start insulating the manifold where the flue connects and use a more highly insulated type of chimney.

Henk
 
I don't mean "too large" of a stove - I only mean too large of a firebox inside the stove.

'Too tall to work well" for some reason is what I am really asking. Although just what defect of performance I might need to be concerned for is still a mystery to me at this point. <g>

That's why I am asking you all. <g>

You mention: "too tall" - is there some problem which the disproportionately tall firebox height creates? Is it bad in some way?

The firebox height is a by-product in my case. I wanted the side wall square tubes to be more vertical than 45º for easy natural convection up through them and I didn't want the firebox too narrow. So with the firebox floor base at 36" width - necessary in order to have the bricked-in width come out to 19" - that required 48" long wall tube lengths.

Then I sized the area above the smoke shelf to 300% of the flue pipe's cross-section area. Because I wanted the flue gas velocity much slower inside the stove than it will be in the actual flue pipe - in order for the surrounding steel to better remove the heat from the flue gas.

No; I do not think I have any texts on woodstove design. I have several relating to fireplace design and building but that seems unrelated in terms of the details I am most curious about.

Oh wait! I have every Mother Earth News issue from #1 to about 1986. I imagine that there might be something related to building one's own wood stove in there somewhere.

BTW: I am placing the secondary air tube manifold directly under the smoke shelf . . . . . well; unless you all tell me to do it otherwise for some reason.

Which raises another question in regard to fire box height - will the high firebox interfere with the idea and perfomance of secondary combustion?

And also: I am thinking of incorporating a small lip (say 1" - 1 1/2") extending down from the rear of the shoke shelf - to better "trap" the gasses which would typically be burned in the secondary combustion process - rather than allow them to be 'whisked' up and away from the secondary air manifold too quickly.

So? A good idea? What do you all think?

PHM
------





BeGreen said:
Too large for what? One design may be too large for a house, but great for the pole barn. The firebox size mentioned is big, but if you are heating and open plan, 3000 sq ft space it might be ok. Or just perfect for the 24' sq cabin that wants to be a sauna.

The firebox seems a bit tall. You probably won't be filling it that high. Will it have two courses of firebrick on the sides? If not, I would lower the height. How far would depend, will there be secondary tubes under the baffle?

PS: Do you have any books on stove design or wood burning? Some early texts by Jay Shelton might be helpful.
Click to expand...
 
Moderator,

I disagree with the merging of questions idea - because it seems common that one question in a combination of questions gets answered / discussed while the others go lacking for response and then are buried several posts behind.

I think that happens because sometimes one is able to answer / discuss one question out of a list of them and does so. Having each question in isolation tends to negate this issue.

In my experience anyway. <g>

It may seem less tidy - but I think individualizing questions fosters a better and likely fuller discussion.

PHM
-----





BeGreen said:
Merged threads so that questions in one aren't answered in another thread.

It's good to preheat the secondary air. if possible.
Click to expand...
 
I would posit that threads that refer to another get more confusing, especially for the next person that might be reading it a few months later. It this thread gets off track, put it back on track. You're in charge of it.

And yes, if the smoke baffle and secondary air is too high, it may be ineffective. You want it mixing preheated air right into the gasses coming off of the wood. One thing you might try is additional baffling above the lower baffle to make the smoke go in a more S shaped path to give up more heat. This is kind of like the tall Morso, Lange and Jotul designs. If you choose this design, be sure to add clean out port(s).
 
BeGreen said:
I would posit that threads that refer to another get more confusing, especially for the next person that might be reading it a few months later. It this thread gets off track, put it back on track. You're in charge of it.

And yes, if the smoke baffle and secondary air is too high, it may be ineffective. You want it mixing preheated air right into the gasses coming off of the wood. One thing you might try is additional baffling above the lower baffle to make the smoke go in a more S shaped path to give up more heat. This is kind of like the tall Morso, Lange and Jotul designs. If you choose this design, be sure to add clean out port(s).
Click to expand...

Completely agree. If there is a very deep or tall "firebox" (hard to say where the real firebox ends and other stove compartments start in a case like this) that provides lots of room for sequential (1) primary combustion, (2) secondary combustion, and (3) additional heat exchange processes, you will want to stage them in that exact order (i.e. 1 -> 2 -> 3). Not 2 and 3 in parallel or (worse) 2 after 3, since the higher the wood gas temperatures upon entering the reburn zone the more complete and clean the burn will be.

If you MUST do (2) after (3), you will probably need to use a catalytic rather than thermal afterburner design. As long as the gases are still hot enough to make the catalyst take off, it will keep itself going. However, as the catalyst ages and loses activity you will be sorry you allowed the primary combustion gases to cool off a bit....

Henk

edit: It would help a great deal if the OP could outline what his highest priorities are; i.e. burning unusually large loads of wood in order to get unusually large total heat outputs OR burning a regular load as completely and cleanly as possible OR burning a regular load at maximum efficiency (plus any reasonable combination of these three extremes). HM
 
Good thinking - a definition of my goals <g>

I started out this time with (whew! let me think as I write <g>) the idea of burning wood to get heat into my cellar as a way of heating the house above it. In the past this has been done to nice effect by heating the cellar to about 80º - which tends to heat the house by radiant floor effect.

I liked doing that with a simple, welded steel, unbaffled box stove and a Heat Reclaimer in the flue pipe for many years. Later I installed a New Mac wood furnace which didn't work as well and didn't heat the cellar. Plus; it's way more complicated.

With the box stove I tried all kinds of things. For a while I piled it all over with scrap steel - heavy angle irons and railroad track in an effort to gain more radiant heating. I also stacked bricks and concrete blocks all around and entirely over it for a few years. I thought about welding 3" vertical pipes all around it to add surface area and the aide convention - but I didn't.

The adding-tubes idea was really the genesis for the present Goldberg I am building. One thought led to another until I settled on the triangle front cross section and the steel tube walls as the best effect with the least amount of materials.

Then you all gave me the idea of adding secondary air and so: secondary combustion. I like the idea of increasing performance / efficiency by means of adding a simple-to-build system with no moving parts.

All design is compromise.

If I have to buy a catalytic unit - and I assume they have a finite lifespan - I don't want to do it. I'd forego the increased efficiency.

But if I can build a better fire box - I will. If lining the combustion chamber with bricks will be better - I will do it. If I can add secondary air tubes - I will.

I guess my primary and basic goal is to convert wood into heat.

Not necessarily at a particularly high rate however.

So: maybe burn regular sized amounts of wood as cleanly as I can arrange to do?

Secondarily I would like to make the stove work as well as I reasonably can (meaning: full of Reason - not inexpensive <g>).

Is that enough of an answer? <g>

PHM
------


PyMS said:
. . . It would help a great deal if the OP could outline what his highest priorities are; i.e. burning unusually large loads of wood in order to get unusually large total heat outputs OR burning a regular load as completely and cleanly as possible OR burning a regular load at maximum efficiency (plus any reasonable combination of these three extremes). HM
Click to expand...
 
Poodleheadmikey said:
Good thinking - a definition of my goals <g>

I started out this time with (whew! let me think as I write <g>) the idea of burning wood to get heat into my cellar as a way of heating the house above it. In the past this has been done to nice effect by heating the cellar to about 80º - which tends to heat the house by radiant floor effect.

I liked doing that with a simple, welded steel, unbaffled box stove and a Heat Reclaimer in the flue pipe for many years. Later I installed a New Mac wood furnace which didn't work as well and didn't heat the cellar. Plus; it's way more complicated.

With the box stove I tried all kinds of things. For a while I piled it all over with scrap steel - heavy angle irons and railroad track in an effort to gain more radiant heating. I also stacked bricks and concrete blocks all around and entirely over it for a few years. I thought about welding 3" vertical pipes all around it to add surface area and the aide convention - but I didn't.

The adding-tubes idea was really the genesis for the present Goldberg I am building. One thought led to another until I settled on the triangle front cross section and the steel tube walls as the best effect with the least amount of materials.

Then you all gave me the idea of adding secondary air and so: secondary combustion. I like the idea of increasing performance / efficiency by means of adding a simple-to-build system with no moving parts.

All design is compromise.

If I have to buy a catalytic unit - and I assume they have a finite lifespan - I don't want to do it. I'd forego the increased efficiency.

But if I can build a better fire box - I will. If lining the combustion chamber with bricks will be better - I will do it. If I can add secondary air tubes - I will.

I guess my primary and basic goal is to convert wood into heat.

Not necessarily at a particularly high rate however.

So: maybe burn regular sized amounts of wood as cleanly as I can arrange to do?

Secondarily I would like to make the stove work as well as I reasonably can (meaning: full of Reason - not inexpensive <g>).

Is that enough of an answer? <g>

PHM
Click to expand...


Aw Shucks, now that I read your very informative reply. I wish we would not have to open the Pandora's box of "radiative floor heating" since this might possibly end up in a food fight between various interested parties in the world of home heating, or at least steer this discussion off the rails in no time....

For years I have tried to take a deep breath and swallow hard whenever someone would raise the topic of "radiant floor heating". Although I believe the use of the term "radiant" to be very misleading in this context, I fully agree that the practical result is a very comfortable type of heat that, for many people, can be well worth the very high price. So why quibble about the terminology?? After all, "a rose by any name still smells as sweet", right??

However, I don't quite see how anyone will be able to discuss your admirable design of a "radiant floor heating" system from the perspective of (radiant + convective + conductive) heat generation and transport without first trying to make the point that the term "radiant" as used for floor heating systems is at best misleading and at worst incorrect.

In other words, in order to have a sensible discussion about your design we better drop the term "radiant" from your floor heating objectives.

There; I have said it. So let's first wait and see if Pandora's box has been seriously breached already or if the members of this forum can still find common ground for a productive discussion.......

Henk

edit: Just wanted to add that I have no commercial ties of any nature with the home heating industry. HM
 
In a food fight - I prefer that my opponents only throw prime filets - rare. And if at all possible - prepared on a Broil Master grille.

OK - what shall we call the process of first heating the floor so that we may heat the space above the floor? <g>

If it's not radiant - what is it?

This all creates a conundrum for me in another way too - I have some hydronic solar panels and will be soon adding some more. About 200 square feet of collector area. This makes so much hot water that I toy with the idea of diverting it to use for space heating. In which case a hydronic floor heating system makes the most sense as it utilizes the lowest temperature "boiler" water.

If I eventually ever staple up all those miles of PEX - I will foil-barrier and foam-board insulate under them. Then, as the floor joists will be insulated - that will remove all my ability to heat the floor with the wood stove.

PHM
------





PyMS said:
Poodleheadmikey said:
Good thinking - a definition of my goals <g>

I started out this time with (whew! let me think as I write <g>) the idea of burning wood to get heat into my cellar as a way of heating the house above it. In the past this has been done to nice effect by heating the cellar to about 80º - which tends to heat the house by radiant floor effect.

I liked doing that with a simple, welded steel, unbaffled box stove and a Heat Reclaimer in the flue pipe for many years. Later I installed a New Mac wood furnace which didn't work as well and didn't heat the cellar. Plus; it's way more complicated.

With the box stove I tried all kinds of things. For a while I piled it all over with scrap steel - heavy angle irons and railroad track in an effort to gain more radiant heating. I also stacked bricks and concrete blocks all around and entirely over it for a few years. I thought about welding 3" vertical pipes all around it to add surface area and the aide convention - but I didn't.

The adding-tubes idea was really the genesis for the present Goldberg I am building. One thought led to another until I settled on the triangle front cross section and the steel tube walls as the best effect with the least amount of materials.

Then you all gave me the idea of adding secondary air and so: secondary combustion. I like the idea of increasing performance / efficiency by means of adding a simple-to-build system with no moving parts.

All design is compromise.

If I have to buy a catalytic unit - and I assume they have a finite lifespan - I don't want to do it. I'd forego the increased efficiency.

But if I can build a better fire box - I will. If lining the combustion chamber with bricks will be better - I will do it. If I can add secondary air tubes - I will.

I guess my primary and basic goal is to convert wood into heat.

Not necessarily at a particularly high rate however.

So: maybe burn regular sized amounts of wood as cleanly as I can arrange to do?

Secondarily I would like to make the stove work as well as I reasonably can (meaning: full of Reason - not inexpensive <g>).

Is that enough of an answer? <g>

PHM
Click to expand...


Aw Shucks, now that I read your very informative reply. I wish we would not have to open the Pandora's box of "radiative floor heating" since this might possibly end up in a food fight between various interested parties in the world of home heating, or at least steer this discussion off the rails in no time....

For years I have tried to take a deep breath and swallow hard whenever someone would raise the topic of "radiant floor heating". Although I believe the use of the term "radiant" to be very misleading in this context, I fully agree that the practical result is a very comfortable type of heat that, for many people, can be well worth the very high price. So why quibble about the terminology?? After all, "a rose by any name still smells as sweet", right??

However, I don't quite see how anyone will be able to discuss your admirable design of a "radiant floor heating" system from the perspective of (radiant + convective + conductive) heat generation and transport without first trying to make the point that the term "radiant" as used for floor heating systems is at best misleading and at worst incorrect.

In other words, in order to have a sensible discussion about your design we better drop the term "radiant" from your floor heating objectives.

There; I have said it. So let's first wait and see if Pandora's box has been seriously breached already or if the members of this forum can still find common ground for a productive discussion.......

Henk

edit: Just wanted to add that I have no commercial ties of any nature with the home heating industry. HM
Click to expand...
 
Poodleheadmikey said:
In a food fight - I prefer that my opponents only throw prime filets - rare. And if at all possible - prepared on a Broil Master grille.

OK - what shall we call the process of first heating the floor so that we may heat the space above the floor? <g>
Click to expand...

Thanks for the humor and for cutting to the quick.
Let's just call it "subfloor heating" or, in your particular case, "subfloor heating by woodstove" or something like that.

If it's not radiant - what is it?
Click to expand...

when you walk bare-feet on subfloor-heated tiles, wood or even carpet the heat is being transferred from the floor to your body by conduction to your foot soles and through contact of the rest of the body with warm air in the form of (micro)convection currents (or even diffusion, especially in case of a carpet floor because there may be few readily measurable air currents). Although the conductive heat transfer to one's bare foot soles can be subjectively the dominant source of heat it will tend to be surpassed by the convective heat received from the air, simply because of the relatively small surface area of one's feet

Finally -- and unavoidably -- there will indeed be some thermal radiation from the floor. If one does the math, however, for typical floor temperatures (unsurprisingly not too different from your skin temperature, or it would NOT be very comfortable to the touch) one will find that the amount of radiation received directly from the floor is much smaller than the heat received from the air in the room, particularly the warm air slowly rising up from the floor below. Moreover, because our skin temperature will only tend to differ from the floor temperature by a handful of degrees, the amount of heat radiated away by the skin might even surpass the amount of radiation received directly from the floor.....

This all creates a conundrum for me in another way too - I have some hydronic solar panels and will be soon adding some more. About 200 square feet of collector area. This makes so much hot water that I toy with the idea of diverting it to use for space heating. In which case a hydronic floor heating system makes the most sense as it utilizes the lowest temperature "boiler" water.

If I eventually ever staple up all those miles of PEX - I will foil-barrier and foam-board insulate under them. Then, as the floor joists will be insulated - that will remove all my ability to heat the floor with the wood stove.

PHM
Click to expand...

There should not be a conundrum created (at least not by my words) in any way. Subfloor heating is a GREAT way of heating. Women especially seem to love it. Perhaps their radiant faces (while walking on such nice warm floors) could have inspired the misnomer ? ;)
So, by putting in the big hydronic subfloor heating system you describe you probably can't go wrong.

For now, the real question is, of course, whether you will be able to transfer enough of the heat generated by your wood stove to the sub-floor to provide the result you are hoping for. In order to estimate some of the key design parameters it would be helpful to have the following information:
(a) how many cords of wood are you willing to burn per month in order to run the stove ?, and
(b) how much heat is needed to heat the living room above the basement ? (perhaps you already know what amount of electric power, gas, oil or LPG, it has taken so far to heat that room to your liking).

Henk
 
Wow; check out the big brain on Henk! <g>

So for my SHBW heating system to heat the floor space above the floor I need to add about 30,000 BTU's to the space per hour when it is 0ºF. outside. Less of course when the outside temperature is higher. 0 BTU's when it is 65º outside.

Making linear assumptions - the average winter temperature is about 33º so let's call it 15,000 BTU's required per hour on average.

Wood averages about 2500 lbs per cord and contains about 15 million BTU's per cord.

So - blah, blah, blah - assume a 50% overall conversion-to-useable-heat efficiency and that means I get about 500 hours of heating per cord of wood burned. 500 hours is about 2/3 of a month. So, with 1/3 of the total requirement provided by natural gas and solar - call it one cord of wood per month on average.

I think I would be willing to burn that amount per month.

Uhhhh . . . . what the hell are we trying to figure out here again? <g>

PHM
-----







PyMS said:
. . . . For now, the real question is, of course, whether you will be able to transfer enough of the heat generated by your wood stove to the sub-floor to provide the result you are hoping for. In order to estimate some of the key design parameters it would be helpful to have the following information:

(a) how many cords of wood are you willing to burn per month in order to run the stove ?, and

(b) how much heat is needed to heat the living room above the basement ? (perhaps you already know what amount of electric power, gas, oil or LPG, it has taken so far to heat that room to your liking).

Henk
Click to expand...
 
Poodleheadmikey said:
Wow; check out the big brain on Henk! <g>
Click to expand...

You wouldn't be trying to make this into a "you must be an even bigger geek than I am" contest; would you now ?? :) :)

So for my SHBW heating system to heat the floor space above the floor I need to add about 30,000 BTU's to the space per hour when it is 0ºF. outside. Less of course when the outside temperature is higher. 0 BTU's when it is 65º outside. Making linear assumptions - the average winter temperature is about 33º so let's call it 15,000 BTU's required per hour on average.
Click to expand...

You need to deliver 15,000 BTU/hr (on average) to the room above the basement. For the sake of argument, let's say you find a way to transport that amount of heat flux from the stove to the ceiling and accross with only 50% loss and you manage to do that in such a way that the losses nicely heat the basement. If so, your stove will need to put out 30,000 BTU/hr on average and 60,000 BTU when it is 0 degrees outside, if I understood your numbers correctly. That kind of output sounds feasible (though not easy), as confirmed by your past experience with the first stove which apparently kept the basement at 80F while warming the ceiling and the room above via subfloor heating.

So, if you have a simple, let's say tongue and groove, ceiling which is also the floor of the room above, and manage to heat the underside enough to get the floor surface inside the room above at 70-75 F, you may have a shot at heating that room well enough if you include the additional heat sources you mentioned. Obviously, the larger the ceiling/floor area and the better it can conduct heat the smaller the temp gradient across that barrier will be. Since you probably do not want to heat the cellar much above 80F, maintaining such a small temperature gradient is not going to be easy, I believe.


Wood averages about 2500 lbs per cord and contains about 15 million BTU's per cord.

So - blah, blah, blah - assume a 50% overall conversion-to-useable-heat efficiency and that means I get about 500 hours of heating per cord of wood burned. 500 hours is about 2/3 of a month. So, with 1/3 of the total requirement provided by natural gas and solar - call it one cord of wood per month on average.

I think I would be willing to burn that amount per month.

Uhhhh . . . . what the hell are we trying to figure out here again? <g>

PHM
Click to expand...

Mostly whether you could indeed be able to produce enough heat. It sounds to me like you might have to burn at a rate of up to 4 cord per month during the coldest days, though.....

Assuming that you can keep the cellar walls and floor well enough insulated to force the lion's share of your wood stove heat to "escape" via the ceiling while keeping the trans-floor temperature gradients small enough, you might be able to prove the common perception that air-mediated subfloor heating is simply too inefficient for residential use wrong for your particular set-up.

Nonetheless, I expect you will be much happier once you are able to make the transition to hydronic sub-floor heating. Are you planning to weld your own internal air/water heat exchanger for the new stove?

Henk
 
Although I do make my own brazed / silver soldered shell & tube heat exchangers - I really don't have a big brain - I am just going to put two cast iron radiators inside my next boiler/woodstove.

I was going to weld up a 'scotch-marine' type of fire tube boiler for myself but it seems like a big PITA. Even though I do have a tube roller with which to install the fire tubes.

BTW: I was just jabbing you a bit before - I like words and languages in general , and in particular; their proper useage.

stephen
----------






PyMS said:
Poodleheadmikey said:
Wow; check out the big brain on Henk! <g>
Click to expand...

You wouldn't be trying to make this into a "you must be an even bigger geek than I am" contest; would you now ?? :) :)

So for my SHBW heating system to heat the floor space above the floor I need to add about 30,000 BTU's to the space per hour when it is 0ºF. outside. Less of course when the outside temperature is higher. 0 BTU's when it is 65º outside. Making linear assumptions - the average winter temperature is about 33º so let's call it 15,000 BTU's required per hour on average.
Click to expand...

You need to deliver 15,000 BTU/hr (on average) to the room above the basement. For the sake of argument, let's say you find a way to transport that amount of heat flux from the stove to the ceiling and accross with only 50% loss and you manage to do that in such a way that the losses nicely heat the basement. If so, your stove will need to put out 30,000 BTU/hr on average and 60,000 BTU when it is 0 degrees outside, if I understood your numbers correctly. That kind of output sounds feasible (though not easy), as confirmed by your past experience with the first stove which apparently kept the basement at 80F while warming the ceiling and the room above via subfloor heating.

So, if you have a simple, let's say tongue and groove, ceiling which is also the floor of the room above, and manage to heat the underside enough to get the floor surface inside the room above at 70-75 F, you may have a shot at heating that room well enough if you include the additional heat sources you mentioned. Obviously, the larger the ceiling/floor area and the better it can conduct heat the smaller the temp gradient across that barrier will be. Since you probably do not want to heat the cellar much above 80F, maintaining such a small temperature gradient is not going to be easy, I believe.


Wood averages about 2500 lbs per cord and contains about 15 million BTU's per cord.

So - blah, blah, blah - assume a 50% overall conversion-to-useable-heat efficiency and that means I get about 500 hours of heating per cord of wood burned. 500 hours is about 2/3 of a month. So, with 1/3 of the total requirement provided by natural gas and solar - call it one cord of wood per month on average.

I think I would be willing to burn that amount per month.

Uhhhh . . . . what the hell are we trying to figure out here again? <g>

PHM
Click to expand...

Mostly whether you could indeed be able to produce enough heat. It sounds to me like you might have to burn at a rate of up to 4 cord per month during the coldest days, though.....

Assuming that you can keep the cellar walls and floor well enough insulated to force the lion's share of your wood stove heat to "escape" via the ceiling while keeping the trans-floor temperature gradients small enough, you might be able to prove the common perception that air-mediated subfloor heating is simply too inefficient for residential use wrong for your particular set-up.

Nonetheless, I expect you will be much happier once you are able to make the transition to hydronic sub-floor heating. Are you planning to weld your own internal air/water heat exchanger for the new stove?

Henk
Click to expand...
 
Poodleheadmikey said:
Although I do make my own brazed / silver soldered shell & tube heat exchangers - I really don't have a big brain - I am just going to put two cast iron radiators inside my next boiler/woodstove.

I was going to weld up a 'scotch-marine' type of fire tube boiler for myself but it seems like a big PITA. Even though I do have a tube roller with which to install the fire tubes.

BTW: I was just jabbing you a bit before - I like words and languages in general , and in particular; their proper useage.

stephen
Click to expand...


Thanks for the reassuring response, Stephen. However, I took no offense whatsoever and greatly enjoyed our discussion.

Before I sign off from this discussion in order to let some other forum members try to get a word in, however, I want to ask you two things:

(1) were you going to put in an OAK? (I hope you do if you want to keep that cellar as toasty as possible); and

(2) are you contemplating an outside or inside boiler? (if the latter, I presume it will be based on a wood gasifier stove design)

Henk
 
What about secondary air systems ?

The incoming secondary air wants to be as hot as possible - yes?

Is so; rather than a u-bend as that other guy on here added, how about a serpentine arrangement? Two u-bends? Say: two heating passes of welded pipe and one pass (the uppermost) with the outlet holes drilled in it. I could have the secondary air piping inlet entering through the rear wall.

Does the secondary air have to be off to start / then on when up to temperature? Or can the secondary air system be pulling air in all the time?

Would there be any benefit to adding a downward 'lip' to the rear edge of the smoke shelf? To kind of 'trap' the escaping wood gas there in order to burn it?

Michael
---------
 
I forgot to mention before - I have the chamber all bricked except for two bricks that I have to cut to fit. Those two are soaking in water now.

65 full sized bricks total.

I took some pics but have no idea how to show them. I could e-mail them if anybody is interested in seeing them.

PHM
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